Small electronic components, including amplifiers, filters, transducers and the like, are employed in a number of devices, particularly in radio frequency (RF) wireless communications, for example. Various types of filters, for example, include acoustic filters, such as surface acoustic wave (SAW) resonator devices containing SAW resonators, and bulk acoustic wave (BAW) resonator devices containing thin film bulk acoustic resonators (FBARs) and solidly mounted resonators (SMRs), for example.
Conventionally, the electronic components on and/or in printed circuit boards (PCBs) are combined in circuit packages and covered with external shields to form discrete shielded packages, referred to as “modules.” The external shields are generally shield layers that cover top and sidewalls of the circuit packages, and provide protection against externally generated electromagnetic radiation (“external electromagnetic radiation”), that may cause electromagnetic interference (EMI), as well as some protection against environmental stresses, such as temperature, humidity and physical impact, for example. That is, to reduce effects of electromagnetic radiation, the circuit package is coated with an electrically conductive shield material layer which is grounded externally or internally to create the shield that is conformal to circuit package. In order to provide protection against the external electromagnetic radiation, the external shield is formed of electrically conductive material, typically metal. The bottom of a circuit package, though, is typically not shielded by the external shield, since the substrate of the PCB itself, together with external connecting pins and pads arranged on the bottom of the substrate and/or various electronic components, transmission lines and other circuitry within the substrate generally provide some external shielding from external electromagnetic radiation. The external shield layers together with the bottom shielding together provide a “global shield” for the module.
For example, the conformal external shield is intended for shielding the circuit package on five sides, but not the sixth side (with the connecting pins/pads), where the conformal externals shield may short to signal pins/pad. However, depending upon coating method and package structure, there is a tendency for the conformal external shield to partially coat the sixth side with overflow around the side edges, which may be referred to as “back-spill.”
Accordingly, there is a need for enhanced shielding among and between electronic components within a shielded circuit package or module, which does not unduly restrict design freedom with regard to placement of the electronic components, size of the module and other features.